1. Field of the Invention
The present invention relates to a method of adjusting parameters for shooting a digital image. More particularly, the present invention relates to a method for adjusting the depth of field when a digital camera is used to shoot images at different object distances according to the object distances in different regions of the image to be shot.
2. Related Art
As the rapid development of digital cameras, the photography is no longer an expensive consumption. The user can take pictures whenever he/she wants to record the memorable moment or scenery. In order to highlight the image to be shot, a technique of shallow depth of field (DOF) is generally adopted to make the object become clear and the overall background become fuzzy, and thus extracting the object to be shot from the background, thereby making the object to be shot become more attractive. The depth of field refers to a distance before or after the object having the clearest image while the imaging definition are still qualified, which is relevant to the focal length, aperture of the lens, object distance, and circle of confusion. Substantially, the larger the aperture is and the higher the focus range is, the shallower the depth of field is.
The effect of the shallow DOF is determined by the relationship among the aperture, focal length, and object distance. The object distance refers to the distance between the lens of the digital camera and the object to be shot. The focal length refers to the distance between the lens and the photosensitive element. Referring to FIG. 1a, it is a schematic view of the relationship between a focal length and an object distance. Generally, the larger the aperture is, the shallower the depth of field is; the longer the focal length is (approaching the telephoto end), the shallower the depth of field is; the closer the object distance (the distance between the lens and the object), the shallower the depth of field is. Referring to FIG. 1b, it is a schematic view of a shallow depth of field (DOF) imaging process.
On the contrary, when taking scenery pictures, a deep depth of field is required when shooting the whole scenery image. At this time, the digital camera needs to be adjusted to a small aperture, short focal length, or long object distance, so as to lengthen the depth of field. Referring to FIG. 1c, it is a schematic view of a deep depth of field (DOF) imaging process.
However, as for a common user, since he/she may not have sufficient knowledge about photograph, he/she cannot further adjust the corresponding parameters of the camera, and as a result, he/she cannot take a satisfactory picture. If selecting the photograph mode of adjusting the digital camera, sometimes, the user may forget to adjust the camera into the corresponding photograph mode. For example, if the macro mode is used to take a scenery picture, the scenery picture is rather fuzzy, and vice versa.